Photosensitive resin composition for optical waveguide formation and optical waveguide

ABSTRACT

A photosensitive resin composition for optical waveguide formation, comprising:
         (A) a di(meth)acrylate having the structure represented by the following general formula (1):       

                         
(wherein R 1  is —(OCH 2 CH 2 ) m —, —(OCH(CH 3 )CH 2 ) m —, or —OCH 2 CH(OH)CH 2 —; X is —C(CH 3 ) 2 —, —CH 2 —, —O—, or —SO 2 —; Y is a hydrogen atom or a halogen atom; m is an integer of 0 to 4);
         (B) a mono(meth)acrylate having the structure represented by the following general formula (2):       
                         
(wherein R 2  is —(OCH 2 CH 2 ) p —, —(OCH(CH 3 )CH 2 ) p —, or —OCH 2 CH(OH)CH 2 —; Y is a hydrogen atom, a halogen atom, Ph-C(CH 3 ) 2 —, Ph-, or an alkyl group having 1 to 20 carbon atoms; p is an integer of 0 to 4; Ph is a phenyl group); and
         (C) a photoradical polymerization initiator. The composition has excellent patterning ability, refractive index, heat resistance, and transmission characteristic.

TECHNICAL FIELD

The present invention relates to a photosensitive resin composition foroptical waveguide formation which is used for fabricating opticalcircuits used in the fields of optical communications and opticalinformation processing, and also relates to an optical waveguidefabricated by using the aforementioned composition.

BACKGROUND ART

Because the multimedia époque has created a demand for increased volumeand speed of information processing in optical communication systems andcomputers, transmission systems using light as a transmission mediumhave been finding application in public communication networks, LAN(local area networks), FA (factory automation), interconnectors betweencomputers, household internal wiring, and the like. Among the elementsconstituting the transmission systems, optical waveguides are the basicstructural elements, for example, in optical devices for realizinghigh-volume information transmission of movies and dynamic images,optical computers, optoelectronic integrated circuits (OEIC), andoptical integrated circuits (optical IC). Optical waveguides have beenactively studied because of a large demand for them. Especially,high-performance and low-cost products are especially required.

Quartz optical waveguides and polymer optical waveguides are known asoptical waveguides.

Among them, quartz optical waveguides have an advantage of a lowtransmission loss. However, quartz optical waveguides have disadvantagesof causing process-related problems which include a high temperaturerequired in the processing of the manufacturing step, and difficultiesencountered in the production of optical waveguides having large surfaceareas.

Further, the advantages of polymer optical waveguides include easinessof processing and a large degree of freedom in material design. For thisreason, the use of polymer materials such as poly(methyl methacrylate),polycarbonate and the like have been studied. However, polymer opticalwaveguides usually have poor heat resistance. For this reason,fluorinated polyimides that have excellent heat resistance andtransmission loss have been widely researched in recent years.

However, when polymer materials are used, it takes a lot of time toproduce polymer optical waveguides, because dry etching is required forforming core portions of polymer optical waveguides as requiredsimilarly in the production of quarts optical waveguides.

Under these circumstances, photocurable materials such as epoxyUV-curable resins having photolithographic capability, and opticalwaveguides using such photocurable materials have been recentlysuggested (for example, see claim 1 of Japanese Patent ApplicationLaid-open (JP-A) No. H6-273631).

As described above, the problems associated with the conventionalpolymer optical waveguides are that the waveguide loss in the region ofa wavelength of 650-1600 nm is comparatively high, heat resistance ispoor, and some of the characteristics required for the opticalwaveguides are unsatisfactory.

In order to resolve these problems, chemical treatment methods of thepolymer such as fluorination or deuteration substitution have beenstudied. When such chemical treatment methods are used, adhesion to thesubstrate degrades, and long-term reliability deteriorates. Also, whenthe chemically treated polymer is used for the core portion, therefractive index may not be increased to the desired level.

DISCLOSURE OF THE INVENTION

The present invention has been created to resolve the above-describedproblems, and an object of the present invention is to provide a resincomposition for an optical waveguide which has excellent physicalproperties such as waveguide loss, refractive index and heat resistance,and an optical waveguide composed of the cured product of such acomposition.

The inventors have conducted a comprehensive study to resolve theabove-described problems and have found that a photosensitive resincomposition, which comprises a photoradical polymerization initiator andtwo different (meth)acrylates having aromatic rings, is perfectlysuitable as a resin for forming an optical waveguide. This finding ledto the creation of the present invention.

Thus, the present invention provides a photosensitive resin compositionfor optical waveguide formation, comprising:

(A) a di(meth)acrylate having the structure represented by the followinggeneral formula (1):

(wherein R¹ is —(OCH₂CH₂)_(m)—, —(OCH(CH₃) CH₂)_(m)—, or —OCH₂CH(OH)CH₂—; X is —C(CH₃)₂—, —CH₂—, —O—, or —SO₂—; Y is a hydrogen atom or ahalogen atom; m is an integer of 0 to 4);

(B) a mono(meth)acrylate having the structure represented by thefollowing general formula (2):

(wherein R² is —(OCH₂CH₂)_(p)—, —(OCH(CH₃)CH₂)_(p)—, or —OCH₂CH(OH)CH₂—; Y is a hydrogen atom, a halogen atom, Ph-C(CH₃)₂—, Ph-, or an alkylgroup having 1 to 20 carbon atoms; p is an integer of 0 to 4; Ph is aphenyl group); and

(C) a photoradical polymerization initiator.

The photosensitive resin composition for optical waveguide formationhaving such a structure has excellent patterning ability during curing,and demonstrates physical properties such as a high refractive index,high heat resistance, and excellent transmission characteristic (i.e.low waveguide loss) when an optical waveguide is formed. Thephotosensitive resin composition can be preferably used as a materialfor forming a core layer and the like of an optical waveguide.

The resin composition of the present invention can be so composed thatthe weight ratio (A/B) of the component (A) to the component (B) is, forexample, 0.3 to 5.0.

Setting this weight ratio within this numerical range improves physicalproperties such as heat resistance and the like to an even betterdegree.

The resin composition of the present invention can be so constitutedthat total amount of the component (A) and the component (B) in thecomposition is 30 wt. % or higher.

Setting this amount within this numerical range improves physicalproperties such as refractive index, waveguide loss and the like to aneven better degree.

The resin composition of the present invention can comprises a(meth)acrylate having 3 or more (meth)acryloyl groups in a molecule.

Using such a component makes it possible to improve heat resistance andthe like to an even higher degree.

The resin composition of the present invention makes it possible toobtain a cured product having a refractive index of 1.54 or higher at25° C. and 824 nm.

The resin composition of the present invention makes it possible toobtain a cured product having a glass transition temperature (Tg) of 80°C. or higher.

Further, the present invention provides an optical waveguide whichcomprises a core layer, and a clad layer formed by lamination on thecore layer, wherein the core layer and/or the clad layer is composed ofthe cured product of the aforementioned resin composition.

The optical waveguide having the above-described structure has physicalproperties such as a high refractive index, high heat resistance,excellent patterning ability, and low waveguide loss.

Further, the present invention also provides a method for manufacturingan optical waveguide, which comprises a step of irradiating theaforementioned resin composition with radiation via a photomask andcuring the resin composition.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described below in greater detail.

The resin composition of the present invention comprises thebelow-explained components (A)-(C) as the constituent components.

In the present specification, the concept of the resin composition ofthe present invention includes both the liquid form prior to curing,which comprises the components (A) to (C), and the form obtained bycuring the liquid composition comprising the components (A) to (C).

The component (A) constituting the resin composition of the presentinvention is a di(meth)acrylate having the structure represented by thefollowing general formula (1):

(wherein R¹ is —(OCH₂CH₂)_(m)—, —(OCH(CH₃)CH₂)_(m)—, or —OCH₂CH(OH)CH₂—;X is —C(CH₃)₂—, —CH₂—, —O—, or —SO₂—; Y is a hydrogen atom or a halogenatom; m is an integer of 0 to 4).

In the formula (1), examples of the halogen atom represented by Yinclude chlorine, bromine, iodine, and fluorine. Among them, bromine ispreferred.

Examples of the component (A) include ethylene oxide-added bisphenol A(meth)acrylic acid ester, ethylene oxide-added tetrabromobisphenol A(meth)acrylic acid ester, propylene oxide-added bisphenol A(meth)acrylic acid ester, propylene oxide-added tetrabromobisphenol A(meth)acrylic acid ester, bisphenol A epoxy (meth)acrylate obtained bythe epoxy ring opening reaction of bisphenol A diglycidyl ether and(meth)acrylic acid, tetrabromobisphenol A epoxy (meth)acrylate obtainedby the epoxy ring opening reaction of tetrabromobisphenol A diglycidylether and (meth)acrylic acid, bisphenol F epoxy (meth)acrylate obtainedby the epoxy ring opening reaction of bisphenol F diglycidyl ether and(meth)acrylic acid, and tetrabromobisphenol F epoxy (meth)acrylateobtained by the epoxy ring opening reaction of tetrabromobisphenol Fdiglycidyl ether and (meth)acrylic acid.

Among them, ethylene oxide-added bisphenol A (meth)acrylic acid ester,ethylene oxide-added tetrabromobisphenol A (meth)acrylic acid ester,bisphenol A epoxy (meth)acrylate obtained by the epoxy ring openingreaction of bisphenol A diglycidyl ether and (meth)acrylic acid, andtetrabromobisphenol A epoxy (meth)acrylate are especially preferred.

Examples of commercial products of the component (A) include Biscoat#700, #540 (manufactured by Osaka Yuki Kagaku Kogyo K. K.), AronixM-208, M-210 (manufactured by To a Gosei K. K.), NK Ester BPE-100,BPE-200, BPE-500, and A-BPE-4 (manufactured by Shin Nakamura Kagaku K.K.), Light Ester BP-4EA, BP-4PA, Epoxy Ester 3002M, 3002A, 3000M, 3000A(manufactured by Kyoeisha Kagaku K. K.), KAYARAD R-551, R-712(manufactured by Nippon Kayaku K. K.), BPE-4, BPE-10, BR-42M(manufactured by Daiichi Kogyo Seiyaku K.K.), Ripoxy VR-77, VR-60,VR-90, SP-1506, SP-1506, SP-1507, SP1509, and SP-1563 (manufactured byShowa Kobunshi K. K.), and Neopol V779, Neopol V779MA (manufactured byNippon Yupika K. K.).

The component (B) constituting the resin composition of the presentinvention is a (meth)acrylate having the structure represented by thefollowing formula (2).

(wherein R² is —(OCH₂CH₂)_(p)—, —(OCH(CH₃)CH₂)_(p)—, or —OCH₂CH(OH)CH₂—; Y is a hydrogen atom, a halogen atom, Ph-C(CH₃)₂—, Ph-, or an alkylgroup having 1 to 20 carbon atoms; p is an integer of 0 to 4; Ph is aphenyl group).

In the formula (2), examples of the halogen atom represented by Yinclude chlorine, bromine, iodine, and fluorine. Among them, bromine ispreferred.

Examples of the component (B) include phenoxyethyl (meth)acrylate,phenoxy-2-methylethyl (meth)acrylate, phenoxyethoxyethyl (meth)acrylate,3-phenoxy-2-hydroxypropyl (meth)acrylate, 2-phenylphenoxyethyl(meth)acrylate, 4-phenylphenoxyethyl (meth)acrylate,2-hydroxy-3-phenoxypropyl (meth)acrylate, p-cumyl phenol ethylene oxidemodified (meth)acrylate, 2-bromophenoxyethyl (meth)acrylate,4-bromophenoxyethyl (meth)acrylate, 2,4-dibromophenoxyethyl(meth)acrylate, 2,6-dibromophenoxyethyl (meth)acrylate, and2,4,6-tribromophenoxyethyl (meth)acrylate.

Among them, phenoxyethyl (meth)acrylate, phenoxyethoxyethyl(meth)acrylate, (meth)acrylate of p-cumyl phenol reacted with ethyleneoxide, and 2,4,6-tribromophenoxyethyl (meth)acrylate are especiallypreferred.

Examples of commercial products of the component (B) include AronixM113, M110, M101, M102, M5700, and TO-1317 (manufactured by To a GoseiK. K.), Biscoat #192, #193, #220, 3BM (manufactured by Osaka Yuki KagakuKogyo K. K.), NK Ester AMP-10G, AMP-20G (manufactured by Shin-NakamuraKagaku K. K.), Light Acrylate PO-A, P-200A, Epoxy Ester M-600A(manufactured by Kyoeisha Kagaku K. K.), and PHE, CEA, PHE-2, BR-30,BR-31, BR-31M, BR-32 (manufactured by Daiichi Kogyo Seiyaku K. K.).

The total amount of the components (A) and (B) in the resin compositionof the present invention is preferably 30 wt. % or higher, morepreferably 40 wt. % or higher, and especially preferably 50 wt. % orhigher. If the amount is 30 wt. % or higher, when the resin compositionof the present invention is used for the core portion of an opticalwaveguide, a higher refractive index and a lower waveguide loss can beobtained.

The weight ratio (A/B) of the component (A) to the component (B) in theresin composition of the present invention is preferably 0.3 to 5.0,more preferably 0.4 to 4. If this weight ratio is 0.3 or higher, theglass transition temperature of the cured product is increased and heatresistance is improved. Moreover, the core layer can be more reliablyformed to the desired shape. Further, if the weight ratio is 5.0 orless, the patterning ability can be improved.

When the core layer of an optical waveguide is fabricated by using theresin composition of the present invention, from the standpoint ofpatterning ability, the components (A) and (B) are preferably acrylatesrather than methacrylates.

The component (C) constituting the resin composition of the presentinvention is a photoradical polymerization initiator. Examples of thecomponent (C) include acetophenone, acetophenone benzylketal,1-hydroxycyclohexyl phenyl ketone,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2,2-dimethoxy-2-phenylacetophenone,xanthone, fluorenone, benzaldehyde, fluorine, anthraquinone,triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone,4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone,benzoin propyl ether, benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one,2-hydroxy-2-methyl-1-phenylpropane-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one,2,4,6-trimethylbenzoyl diphenylphosphine oxide, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide.

Examples of commercial products of the component (C) include Irgacure184, 369, 651, 500, 819, 907, 784, 2959, CGI1700, CGI1750, CGI11850,CG24-61, Darocur 1116, 1173 (manufactured by Ciba Specialty ChemicalsCo., Ltd.), Lucirin LR8728 (manufactured by BASF Co.), and Uvecryl P36(manufactured by UCB Co.).

The component (C) can be used alone, or can be used in combination oftwo or more thereof to improve the patterning ability.

The weight ratio of the component (C) in the resin composition of thepresent invention is usually 0.01 to 10 wt. %, preferably 0.1 to 7 wt.%. When the weight ratio is 10 wt. % or less, curing characteristic,transmission characteristic, patterning ability, and handleability canbe improved. Furthermore, when the weight ratio is 0.01 wt. % or more,patterning ability and mechanical characteristics of the cured productcan be improved, and the decrease in curing rate can be prevented.

In the present invention, a compound having a (meth)acryloyl group orvinyl group (sometimes referred to hereinbelow as “unsaturated monomer”with the proviso that compounds identical to the components (A) and (B)are excluded) can be used as an optional component in addition to thecomponents (A) and (B). Among them, a (meth)acrylate having three ormore (meth)acryloyl groups is preferably used.

Examples of the (meth)acrylate having three or more (meth)acryloylgroups include (meth)acrylates of polyhydric alcohols having three ormore hydroxyl groups. Examples of such (meth)acrylates includetrimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,trimethylolpropane trioxyethyl (meth)acrylate,tris(2-acryloyloxyethyl)isocyanurate, and pentaerythritol polyacrylate.These compounds may be used individually or in combinations of two ormore thereof.

Examples of commercial products of the (meth)acrylate having three ormore (meth)acryloyl groups include Aronix M305, M309, M310, M315, M320,M350, M360, and M408 (manufactured by To a Gosei K. K.), Biscoat #295,#300, #360, GPT, 3PA, #400 (manufactured by Osaka Yuki Kagaku Kogyo K.K.), NK Ester TMPT, A-TMPT, A-TMM-3, A-TMM-3L, A-TMMT (manufactured byShin-Nakamura Kagaku K. K.), Light Acrylate TMP-A, TMP-6EO-3A, PE-3A,PE-4A, DPE-6A (manufactured by Kyoeisha Kagaku K. K.), and KAYARADPET-30, GPO-303, TMPTA, TPA-320, DPHA, D-310, DPCA-20, and DPCA-60(manufactured by Nippon Kayaku K. K.).

Examples of other unsaturated monomers include vinyl monomers such asN-vinyl pyrrolidone, N-vinyl caprolactam, vinyl imidazole, and vinylpyridine; isobornyl (meth)acrylate, bornyl (meth)acrylate,tricyclodecanyl (meth)acrylate, dicyclopentanyl (meth)acrylate,dicyclopentenyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl(meth)acrylate, 4-butylcyclohexyl (meth)acrylate, acryloyl morpholine,2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl(meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl(meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl(meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl(meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl(meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate,isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate,butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate,polyethylene glycol mono(meth)acrylate, polypropylene glycolmono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl(meth)acrylate, methoxypolyethylene glycol (meth)acrylate,methoxypolypropylene glycol (meth)acrylate, diacetone (meth)acrylamide,isobutoxymethyl (meth)acrylamide, N, N-dimethyl (meth)acrylamide,t-octyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate,diethylaminoethyl (meth)acrylate, 7-amino-3,7-dimethyloctyl(meth)acrylate, N,N-diethyl (meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, hydroxybutylvinyl ether, laurylvinyl ether, cetylvinylether, 2-ethylhexylvinyl ether and monofunctional monomers representedby the following formulas (3), (4)

(wherein R³ is a hydrogen atom or a methyl group; R⁴ is an alkylenegroup having 2 to 8 carbon atoms; s is an integer of 1 to 8).

(wherein each of R⁵ and R⁷ is independently a hydrogen atom or a methylgroup; R⁶ is an alkylene group having 2 to 8 carbon atoms; t is aninteger of 1 to 8).

Examples of an unsaturated monomer having two (meth)acryloyl groups orvinyl groups include alkyldioldiacrylates such as1,4-butanedioldiacrylate, 1,6-hexanedioldiacrylate and1,9-nonanedioldiacrylate, polyalkylene glycol diacrylates such asethylene glycol di(meth)acrylate, tetraethylene glycol diacrylate, andtripropylene glycol diacrylate, neopentylglycol di(meth)acrylate, andtricyclodecane methanol diacrylate.

Examples of commercial products of those compounds include Aronix M120,M-150, M-156, M-215, M-220, M-225, M-240, M-245, and M-270 (manufacturedby To a Gosei K. K.), AIB, TBA, LA, LTA, STA, Biscoat #155, IBXA,Biscoat #158, #190, #150, #320, HEA, HPA, Biscoat #2000, #2100, DMA,Biscoat #195, #230, #260, #215, #335HP, #310HP, #310HG, #312(manufactured by Osaka Yuki Kagaku Kogyo K. K.), Light Acrylate IAA,L-A, S-A, BO-A, EC-A, MTG-A, DMP-A, THF-A, IB-XA, HOA, HOP-A, HOA-MPL,HOA-MPE, Light Acrylate 3EG-A, 4EG-A, 9EG-A, NP-A, 1,6HX-A, DCP-A(manufactured by Kyoeisha Kagaku K. K.), and KAYARAD, TC-110S, HDDA,NPGDA, TPGDA, PEG400DA, MANDA, HX-220, HX-620 (manufactured by NipponKayaku K. K.), FA-511A, 512A, 513A (manufactured by Hitachi Kasei K.K.), VP (manufactured by BASF Co.), and ACMO, DMAA, DMAPAA (manufacturedby Kohjin K. K.).

An oligomer or polymer such as polyurethane (meth)acrylate, polyester(meth)acrylate, and polyepoxy (meth)acrylate may be additionally blendedwith the resin composition of the present invention.

A photosensitizer can be additionally blended with the resin compositionof the present invention.

Examples of photosensitizers include triethylamine, diethylamine,N-methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid,4-dimethylaminobenzoic acid methyl, 4-dimethylaminobenzoic acid ethyl,and 4-dimethylaminobenzoic acid isoamyl. Examples of commercial productsof photosensitizers include Ubecryl P102, 103, 104, 105 (manufactured byUCB Co.).

Examples of various additives, which can be added in addition to theabove-described components in case of need, include antioxidants, UVabsorbers, photostabilizers, silane coupling agents, surfacemodification agents, thermal polymerization inhibitors, leveling agents,surfactants, colorants, preservatives, plasticizers, lubricants,solvents, fillers, antiaging agents, wetting improving agents, andparting agents.

Examples of commercial products of antioxidants include Irganox 1010,1035, 1076, 1222 (manufactured by Ciba Specialty Chemicals), Antigen P,3C, FR, GA-80 (manufactured by Sumitomo Kagaku Kogyo K. K.).

Examples of commercial products of UV absorbers include Tinuvin P, 234,320, 326, 327, 328, 329, 213 (manufactured by Ciba Specialty Chemicals),Seesorb 102, 103, 110, 501, 202, 712, 704 (manufactured by Shipro KaseiK. K.).

Examples of commercial products of photostabilizers include Tinuvin 292,144, 622LD (manufactured by Ciba Specialty Chemicals), Sanol LS770(Sankyo K. K.), Sumisorb TM-061 (Sumitomo Kagaku Kogyo K. K.).

Examples of silane coupling agents include γ-aminopropyltriethoxysilane,γ-mercaptopropyltrimethoxysilane, andγ-methacryloxypropyltrimethoxysilane. Examples of commercial productsinclude SH6062, 6030 (manufactured by Toray Dow Corning Silicone Co.),KBE903, 603, 403 (manufactured by Shin-Etsu Kagaku Kogyo K. K.).

Examples of surface modification agents include silicone additives suchas dimethylsiloxane polyether. Examples of commercial products includeDC-57, DC-190 (manufactured by Dow Corning Co.), SH-28PA, SH-29PA,SH-30PA, SH190 (manufactured by Toray Dow Corning Silicone Co.), KF351,KF352, KF353, KF354 (manufactured by Shin-Etsu Kagaku Kogyo K. K.),L-700, L-7002, L-7500, FK-024-90 (manufactured by Nippon Unicar K. K.).

Examples of commercial products of parting agents include PRISURF A208F(manufactured by Daiichi Kogyo Seiyaku K. K.).

The resin composition of the present invention can be manufactured bymixing the aforementioned components by the usual method. The viscosityof the resin composition of the present invention that is thus preparedis 100-20,000 cp/25° C., preferable 300-10,000 cp/25° C., morepreferably 400-5,000 cp/25° C. If the viscosity is too high, coatingnon-uniformity or waving occurs when the resin composition is coated ona substrate, or the patterning ability is degraded and the designedshape cannot be obtained when a core layer is formed. Conversely, if theviscosity is too low, the desired film thickness is difficult to obtain.Moreover, the patterning ability is sometimes degraded.

The cured product of the resin composition of the present invention thatis obtained by curing with radiation preferably has the followingproperties.

When the cured product of the resin composition of the present inventionis formed as a core layer of an optical waveguide, the refractive indexat 25° C. and a wavelength of 824 nm is preferably 1.54 or more, morepreferably 1.55 or more. If the refractive index is less than 1.54, whena waveguide is formed by using the resin composition of the presentinvention for the core layer, the desired transmission loss sometimescannot be obtained.

The cured product of the resin composition of the present inventionpreferably has a glass transition temperature of 80° C. or higher, morepreferably 90° C. or higher. If the glass transition temperature is lessthan 80° C., a sufficient heat resistance of the optical waveguidesometimes cannot be ensured. The “glass transition temperature” asreferred to herein is defined as the temperature at which the losstangent at an oscillation frequency of 10 Hz exhibits a maximum value inthe resonance-type apparatus for measuring dynamic viscoelasticity.

EXAMPLES

The present invention will be described hereinbelow in greater detailbased on experimental examples. However, the present invention is notlimited to those experimental examples (Examples), and can be modifiedin a variety of ways within the scope defined by the claims.

Examples 1-7 Comparative Examples 1-3

Liquid curable compositions were obtained by mixing the componentsdescribed in Table 1 and conducting stirring for one hour, whilecontrolling the temperature at 50-60° C. In Table 1, the amounts of thecomponents are described as parts by weight.

<Evaluation Methods>

-   1. Evaluation of Refractive Index

The refractive index at 824 nm was measured by the following method.First, a resin composition layer was formed by coating a liquid curablecomposition to a thickness of 7 μm on a silicon wafer substrate having athickness of 4 inches by using a spin coater, while adjusting therotation speed and time. Then, the resin composition layer wasirradiated from a mask aligner with UV rays at 1.0 J/cm² in a nitrogenatmosphere, and a cured film was obtained. Then, the refractive index(824 nm, 25° C.) of the cured film was measured by using a prism couplermanufactured by Nippon Metricon Co.

-   2. Evaluation of Glass Transition Temperature

A resin composition layer was formed by coating a resin composition to athickness of 60 μm on a glass substrate by using an applicator. Then,the resin composition layer was irradiated with UV rays at 1.0 J/cm² byusing a conveyor-type UV irradiation apparatus in a nitrogen atmosphere,and a cured film was obtained. Then, the dependence of the loss tangentof the cured film on temperature was measured by using a resonance-typeapparatus for measuring dynamic viscoelasticity, while applyingoscillations having an oscillation frequency of 10 Hz. The glasstransition temperature was defined as the temperature at which themaximum value of the loss target was obtained.

-   3. Evaluation of Patterning Ability

A resin composition layer was formed by coating a liquid curablecomposition to a thickness of 50 μm on a silicon wafer substrate havinga thickness of 4 inches by using a spin coater, while adjusting therotation speed and time. Then, the resin composition layer wasirradiated from a mask aligner with UV rays at 1.0 J/cm² in an airatmosphere via a photomask having a branch-free and linear shape andhaving a width of 50 μm. The resin composition was then developed for 3minutes by using acetone, and the substrate was heated for 10 minutes inan oven having a fixed temperature of 70° C.

The pattern obtained was observed under an optical microscope. The casein which the target core shape (50 μm±1 μm) was obtained was denoted by“⊚”, the case in which the shape was within a range of 50 μm±2 μm wasdenoted by “◯”, and the case in which the shape was outside the range 50μm±2 μm was denoted by “X”.

4. Evaluation of Transmission Loss

ELC2500 (Clear) (manufactured by ELECTRO-LITE Corporation, N_(D)²⁵=1.515) was coated on a silicon wafer substrate having a thickness of4 inches by using a spin coater, while adjusting the rotation speed andtime. Then, the coated layer was irradiated from a mask aligner with UVrays at 1.0 J/cm² in an air atmosphere. The resin composition was thencoated to a thickness of 50 μm on the substrate by using a spin coater,and the coated layer was irradiated with UV rays at 1.0 J/cm² in an airatmosphere via a photomask having a branch-free and linear shape andhaving a width of 50 μm. The irradiated coated layer was developed for 3minutes by using acetone, and the substrate was heated for 10 minutes inan oven having a fixed temperature of 70° C. Then, the ELC2500 (Clear)was again coated on the substrate to a thickness of 50 μm, and thesubstrate was irradiated with UV rays to obtain a channel waveguide.

The end surface of the waveguide was cleaved and cut, light having awavelength of 850 nm was introduced via a multimode fiber (diameter: 50μm), and the waveguide loss was measured by a cut-back method. Themeasurement method was implemented by conducting 4-point measurements atan interval of 1 cm in a 5 cm-length portion of the waveguide. The lightintensity obtained was plotted against the waveguide length, and theloss value was calculated from the inclination thereof. The case inwhich the loss value obtained was 0.5 dB/cm or less was denoted by “◯”,and the case in which it was higher than 0.5 dB/cm was denoted by “X”.

The results obtained are shown in Table 1. The components presented inTable 1 are as follows.

-   V779: Neopol V779 (manufactured by Nippon Yupika K. K.)

(compound name: tetrabromobisphenol A epoxy acrylate)

-   V779MA: Neopol V779MA (manufactured by Nippon Yupika K. K.)

(compound name: tetrabromobisphenol A epoxy dimethacrylate)

-   PEA: New Frontier PHE (manufactured by Daiichi Kogyo Seiyaku K. K.)

(compound name: phenoxyethyl acrylate)

-   PEMA: Light Ester PO (manufactured by Kyoeisha Kagaku K. K.)

(compound name: phenoxyethyl methacrylate)

-   BR-31: New Frontier BR-31 (manufactured by Daiichi Kogyo Seiyaku K.    K.)

(compound name: tribromophenoxyethyl acrylate)

-   IRG184: Irgacure 184 (manufactured by Ciba Specialty Chemicals Co.,    Ltd.)

(compound name: 1-hydroxy-cyclohexyl phenyl ketone)

-   IRG651: Irgacure 651 (manufactured by Ciba Specialty Chemicals Co.,    Ltd.)

(compound name: 2,2-dimethoxy-1,2-diphenylethane-1-on)

-   IRG369: Irgacure 369 (manufactured by Ciba Specialty Chemicals Co.,    Ltd.)

(compound name:2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1)

-   IRG907: Irgacure 907 (manufactured by Ciba Specialty Chemicals Co.,    Ltd.)

(compound name:2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropane-1-on)

-   M315: Aronix M315 (manufactured by To a Gosei K. K.)

(compound name: tris(2-acryloyloxyethyl)isocyanurate)

-   DPHA: (manufactured by Nippon Kayaku K. K.)

(compound name: dipentaerythritol hexaacrylate)

-   IBXA: (manufactured by Osaka Yuki Kagaku K. K.)

(compound name: isobornyl acrylate)

-   IBXMA: (manufactured by Osaka Yuki Kagaku K. K.)

(compound name: isobornyl methacrylate)

-   ACMO: (Kohjin K. K.)

(compound name: acryloyl morpholine)

-   SA1002: Mitsubishi Kagaku K. K.

(compound name: tricyclodecane dimethanol diacrylate).

TABLE 1 Name of commercial Examples Comparative Examples Componentproduct 1 2 3 4 5 6 7 1 2 3 A V779 23 30 18 50 18 18 58 V779MA 18 B PEA10 20 10 PEMA 10 10 10 10 BR-31 25 10 32 32 30 32 32 48 C IRG184 3 3 3 33 1 3 3 3 IRG651 1 IRG369 0.5 IRG907 0.5 other M315 16 10 25 25 25 25 1616 30 DPHA 5 5 5 5 5 5 5 10 IBXA 10 10 10 IBXMA 10 ACMO 16 10 16 16 10SA1002 5 40 5 5 50 Total amount (parts by weight) 103 103 103 103 103101.5 101.5 103 103 103 Total amount of (A) and (B) 56 39 58 58 97 59 5956 56 0 in composition (wt. %) Weight ratio of (A)/(B) 0.66 3.00 0.430.43 1.00 0.43 0.43 — — — [Properties of liquid] 1000 1000 800 900 4000800 800 300 7000 2000 Viscosity (mPa · S) [Properties of cured body]1.56 1.55 1.56 1.56 1.59 1.56 1.56 1.56 1.56 1.51 Refractive index 824nm Tg (° C.) 109 164 126 140 75 126 126 63 172 153 Patterning ability ⊚⊚ ⊚ ◯ ⊚ ⊚ ⊚ ⊚ X X Transmission characteristic ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ X

From Table 1, it is clear that the resin composition of the presentinvention (Examples 1 to 7) has excellent patterning ability when acured product is formed, and demonstrates excellent refractive index,heat resistance, and transmission characteristic (low waveguide loss)when an optical waveguide is formed.

On the other hand, in Comparative Example 1, because component (A) isnot present, heat resistance is poor. In Comparative Example 2, becausecomponent (B) is not present, patterning ability is poor. In ComparativeExample 3, because components (A) and (B) are not present, patterningability and transmission characteristic are poor.

1. A photosensitive resin composition for optical waveguide formation,comprising: (A) a di(meth)acrylate having the structure represented bythe following general formula (1):

(wherein R¹ is —(OCH₂CH₂)_(m)—, —OCH(CH₃)CH₂)_(m)—, or —OCH₂CH(OH)CH₂—;X is —C(CH₃)₂—, —CH₂—, —O—, or —SO₂—; Y is a hydrogen atom or a halogenatom; m is an integer of 0 to 4; (B) a mono(meth)acrylate having thestructure represented by the following formula (2):

(wherein R² is —OCH₂CH₂)_(p)—, —OCH(CH₃)CH₂)_(p)—, or —OCH₂CH(OH)CH₂—; Yis a hydrogen atom, a halogen atom, Ph-C(CH₃)₂—, Ph-, or an alkyl grouphaving 1 to 20 carbon atoms; p is an integer of 0 to 4; Ph is a phenylgroup; (C) a photoradical polymerization initiator; andtris(2-acryloyloxyethyl)isocyanurate, wherein the weight ratio (A/B) ofsaid component (A) to said component (B) is 0.3 to 5.0.
 2. Thephotosensitive resin composition for optical waveguide formationaccording to claim 1, wherein the total amount of said component (A) andsaid component (B) in said resin composition is 30 wt. % or higher. 3.The photosensitive resin composition for optical waveguide formationaccording to claim 2, wherein said total amount is 40 wt.% or higher. 4.The photosensitive resin composition for optical waveguide formationaccording to claim 2, wherein said total amount is 50 wt.% or higher. 5.The photosensitive resin composition for optical waveguide formationaccording to claim 1, wherein the amount added of saidtris(2-acryloyloxyethyl) isocyanurate is 10 to 25% by weight.
 6. Thephotosensitive resin composition for optical waveguide formationaccording to claim 1, wherein the refractive index of the cured productof said resin composition at 25° C. and 824 nm is 1.54 or higher.
 7. Thephotosensitive resin composition for optical waveguide formationaccording to claim 6, wherein said refractive index is 1.55 or higher.8. The photosensitive resin composition for optical waveguide formationaccording to claim 1, wherein the glass transition temperature (Tg) ofthe cured product of said resin composition is 80° C. or higher.
 9. Thephotosensitive resin composition for optical waveguide formationaccording to claim 8, wherein said glass transition temperature is 90°C. or higher.
 10. The photosensitive resin composition for opticalwaveguide formation according to claim 1, wherein component (A)comprises ethylene oxide-added bisphenol A (meth)acrylic acid ester,ethylene oxide-added tetrabromobisphenol A (meth)acrylic acid ester,bisphenol A epoxy (meth)acrylate obtained by the epoxy ring openingreaction of bisphenol A diglycidyl ether and (meth)acrylic acid, ortetrabromobisphenol A epoxy (meth)acrylate.
 11. The photosensitive resincomposition for optical waveguide formation according to claim 1,wherein component (B) comprises phenoxyethyl (meth)acrylate,phenoxyethoxyethyl (meth)acrylate, (meth)acrylate of p-cumyl phenolreacted with ethylene oxide, or 2,4,6-tribromophenoxyethyl(meth)acrylate.
 12. The photosensitive resin composition for opticalwaveguide formation according to claim 1, wherein said weight ratio is0.4 to
 4. 13. The photosensitive resin composition for optical waveguideformation according to claim 1, wherein components (A) and (B) areacrylates.
 14. The photosensitive resin composition for opticalwaveguide formation according to claim 1, wherein component (C) ispresent in an amount of 0.01 to 10 wt.%.
 15. The photosensitive resincomposition for optical waveguide formation according to claim 1,wherein component (C) is present in an amount of 0.1 to 7 wt.%.
 16. Thephotosensitive resin composition for optical waveguide formationaccording to claim 1, and having a viscosity of 400-5,000 cp/25° C. 17.An optical waveguide comprising a core layer, and a clad layer formed bylamination on said core layer, wherein said core layer and/or said cladlayer is composed of the cured product of the resin composition ofclaim
 1. 18. A method for manufacturing an optical waveguide, comprisinga step of irradiating the resin composition of claim 1 with radiationvia a photomask and curing said resin composition.